Photoelectric cell



Jan. 14 1947,

IE. LIDOW PHOTOELECTRIC CELL Filed Aug. 3, 1942 PLATI H U M SELENIUM PLRYINUM Ano eoLD CADMIUM f ALUMINUM S S EM mm AKO PO U M www TIN M.. PMF- DCSaM N1 MM uwm www.: o `w u n Gc IRON PLATINUM ELINIUM OX IDE C Mmmm CADMIUM omni:

PLE 'I'IHUNF .SELENIUM leon . 3Q/e /00M@ INVENTOR.

si 5' p ATTORNEY.

'a barrier layer of Patented Jan. 14, 1947 UNITED STATES PATENT orifice Pno'roELncTmc onu. Erie Liaew, Les Angeles, oeuf., assigner te Selenium Corporation of America, Calif., a corporationof California Les Angeles,

Application August 3, 1942, semi Ne. 453,392 3 claims. (ci. 13s-39) This invention relates to photoelectric cells of the barrieror blocking-layer type.

In the manufacture of cells comprising a. base plate of iron, a layer of selenium, a layer of'c'admium, and an outer electrode of platinum or other noble metals, difficulty is experienced in producing cells of uniform characteristics, de-V spite the greatest care. The uniformity. of cells of this type has been found to vary from cell to cell, and the previous manufacturing processes for cells of this type result in a large number of discards because the cells produced do not have the required characteristics. j l

It is therefore an object of the present invention to increase the uniformity of photoelectric cells of this type.

One ofthe reasons for this non-uniformity of an electric current of high enough intensity toburn out the shorts. However, this treatment is not always positive in its results.

. It is therefore a further object of theipresent invention to provide a method for the production lofphotoelectric'elements.of the type described which does not have a tendency to produce shorts during the process of manufacture.

called barrier layer between the selenium and the cadmium. Various methods of causing the f or'- mation ofithis barrier layer have been proposed and practicedy and -from what is known ,of the action of the cells it would appear that avery large proportion of the non-uniformity of the i response of the cells is a result of a non-uniform It is therefore a further object of the present invention to provide a method for production of greater uniformity than has been producedfin the past'. i

It is afurther object of the present invention to provide a method of producing photoelectric cells of the barrier layer type which will as`sure` uniformity of.` the barrier layer both on the same cell and from cell to cell.

`Another aspect of thejpresent invention lies in the improvement ofthe translucent electrode.

Platinum, which is ofneutral gray by transmitted light, is .often used for this electrode. Cells layer or else merely penetrating utilizing gold electrodes have a comparatively high output. This has been attributed to the high conductivity of gold and its position in the contact potential table. However, a gold electrode acts as a green lter, and therefore alters the spectral characteristics of the cell in which it is used. Another disadvantage of gold, in this connection, is the high temperature coefficient of cells with gold electrodes, as compared with those employing platinum electrodes.

- It is therefore a further object of the present invention to provide a new type of outer electrode which has satisfactory spectral characteristics, and in which the resistance of the outer electrode is comparatively low.

It isa further object of the present invention to provide a cell of the nature described with a small temperature coeiiicient.

l O ne of the most important factorsv in the prog duction of these cells is the formation of the so- This invention possesses many other advantages and has other objects Vwhich maybe made more easily apparent from a consideration of the embodiments thereof, shown in the drawing accompanying and forming part of the present specification. These forms willnow be described in detail, illustrating the general principles of the invention; but it isto be understood that this detailed description is not to be taken in a limiting sense, since the scope of the invention is best dened by the appended claims.

Referring now to the drawing:

Figure 1 is a view of one form of Vapparatus for practicing the present invention;

Figure 2 is a bottom vlewof a cathode utilized in the practice vof the present invention;

Figure 3 is asimilar view of another form of cathode; Y

Figure 4 is a similar view of still another form of cathode;

Figure 5 is a section of one form of cell produced by the present invention; and

Figure 6 is asimilar section of a modified form v of cell.

The selenium is most The preliminary treatment leading to the manufacture of the present cell is similar to that practiced yin .the past. A plate of metal, prefer- A 220 C. Selenium in mechanical pressure at a temperature of between and 140 C. This pressing operation is carried out in a'press which presents a smooth pressure either powdered or molten form is applied to the heated plate. The plate is l' thereafter quickly cooled and then subjected to surface to the selenium, resulting in the development of a smooth surface on the selenium, and is` carried on for a suflicient length of time to convert the amorphous selenium into a semi-metal.. lic form and cause it to adhere strongly to the base plate. In this condition the unit is easily removed from the press.

The next step as taught by the prior art is the K annealing of the cell by heat treatment at a temperature between 170 and 220 C., in a suitable oven. Such annealing results in the conversion of the selenium into a crystalline form. It also results in the development of part of the blocking layer, because of oxidation of the selenium surface. However, the variable humidity of the air Within the oven, together with lack of control over itsA composition, circulation, and other factors results in an extremely variable barrier layer at sputtering action is carried on to produce a transparency of-the deposited lm of about '70%.

After .the deposit of the selenium, the disc I2 is rotated to bring the cadmium element Il above the support Il. The sputtering potential is applied to the cadmium cathode, the current density and flashing intervals being selected to bring the l temperatureof the disc to 140 C. This causes a this point. For this reason, the barrier layer is often increasedin uniformitybytreatment of the selenium in a glow discharge chamber with oxy.:4

gen. As alvariation or supplement to this procedure, a cadmium layer-is often sputtere'd onto theV selenium surface in the presence of water vapor,-whichnresult`s inthe development' of a layer of selenium and cadmiumoxides.

The present invention contemplates a? new methodvof -producing a highly uniform blocking layer. The process may ,be carried out ini an apparatus such as that shown in Figure `l.

support I`I, upon which the selenium coated'disc D is placed, with its seleniumsurface facing upwardly. Thecathodes used in sputtering are mounted 'on a disc I2 ofv heat resisting'glas's or other suitable insulating 4rmaterial fmountedbt'r means of the pivot I3 forrotation within the jar. A :segment I4 of magnetic `material is mounted onlthedisc l2 lto kfacilitate rotation' of the disc bysmeans of a magnet I5 exterior of lthe Jar.'

The chamber I0, which is a vacuum jar properlyy equipped forv sputtering operations, contains alaying on of a film of cadmium and cadmium oxides.

. The 140 C. temperature may be measured in various conventional ways. For instance, a small strip of metal, such as Newtons alloy, with melting lpoint at approximately 140 C., may be placed onthe upper side of the disc I2. The melting of the metal, clearly visible through the glass jar, will indicate when the temperature of.140 C. is reached. A1. alternate method is to use colored wax marks which change 4colors at speciedtemperatures; These waxes are commercially available. Other temperature measuring means' could be employed, such as a thermo-couple connected to the plate, or a thermometer in contact with the plate could be used with little difficulty.

After thecompletion of the cadmium sputtering, the disc l2 is again rotated to bring the third cathode I8`in place. The composition of this cathode is a novel feature'of myv invention. It has essentially a platinum and gold surface, obtained by the use of gold' inserts in the platinum, the area of gold being about of the area of the platinum. Application of a sputtering potential results in a deposit of the gold and platinum together. yThis sputtering action is carried on by As shownin` igure' 2,1the sputtering cathodes f may be in the form `of metallic discsl i6, Il and 18, and are mounted .on the undersldeof the disc :|2,zso.ithatby rotating vthe-disc,"any one of these cathodes can Ibe moved Vifntosputtering pol-1 sition over the cell :supported'onithetablelfhl The cathodes are ,connected :toac'ontact' elements I9 on'the reversevside of the'disc.' 'A brush 20 selectively engagesthe contacts-"Iii,:tov conduct` the "sputtering". currentto` thefelement directly above'the supportillw yAfter the-selenium coated sure broughtxdown :to about i 300 microns, and

fdisc; D is' placedY` on the table Il, the jar is sealed oil and themes-H'- the sputtering current applied to one ofthe cath f1 odes. For tlflezv first operation; the 'sputteringis carried on by means'yof .the cathode. rl6,-which'is of ,seleniunlv The'gsputtering is: don by? flashes,

the current and intervals being selected to raise: 1

the temperatureaoffthe disci to 'about- 1405 Cgi This eleyatedjtemperature and:vv subsequent operations cause ,-.ftlieA :formationff ".of` a highly-2 'satisfactoryj ,It has .b'een'tfoundfrfthatr vinv order ftofproduce' af satisfactoryxblocking.layer, this -st'epf andothers, i must-jxbesregulatedU-innsuch avr'nanne'rthat f* the ftrans'parencv fo'ttlie'nlm-14 laidf Edown 'can be con sputteregona-thei grass :enmity-:fuesesfor' aT suit-1f able meter 23, and, a source of light, first timing the flashes to avoid extensive heating of the cell. The ytransparency of the three sputtered on layers is' notpermitted to drop below' about' 20%. Y The resulting cell is shown in Figure 5. *A base of iron -50 carries a" selen'uin'layebi 'which is `applied by the conventional methods well known in the art. Immediately overlying this is a sput-v tered on layer of selenium and selenium oxides i 52, and on top ofLthatva similar laye'rf5'3 of'cad'- mium and oxides thereof. S'Thetop layer `54 is a homogeneous layer of platinum and gold.

In'the abovedescription, the'st'epof anneal-H ing was mentioned. This'annealingpracticed.inj the pastin' a thermostatically"controlled .ovenjr' at atmospheric lpressure resultedinthe formation. of the nucleus of the blocking Vlayer'. However,"

the conditions v"within a the'rmostatic'allyv con?` trolled oven arediilicultfto 'ciontrolyand theAvari-j 'ations in humidity,cntaminationvof vthe air ,andff other factors Vseriously*affect thecharacterv of the 1 Ablocking layer nucleus Aiormedf'in*the oven These factors result in non-uniform ffnuclei, and the resultigcells are `as 4a'reSult very irregular. i :A Vlarge number of 'them have lvery little "outp only a few being extremelyv eicient;"

As the conditionsV within the vacuum cathode shown in Figure 3 is utilized. Instead of 'a selenium electrode, an aluminum electrode 25 is utilized together with a cadmium ,electrode 26 and a combination platinum and gold electrode 21. The selenium coated disc is supported about an inch from the cathode. The aluminum cathode is positioned opposite the selenium disc and a potential applied to this cathode. The potential should be high enough to raise the t'em- A perature of the Iselenium coated discv to 200 C. It hasbeen found' that the pressure in the jar, the sputtering potential, and the duration of the flashes, determine the length of time necessary to complete the annealing process. subjecting the selenium coated disc to this potential does not result in the deposit of any material, but merely changes the nature of the selenium on the disc. Aluminum is selected for thev cathode as it does not sputter under the potentials and current densities suitable for raising the temperature of the disc to the necessary point. After complelion of annealing, the turn table may be rotated to bring the cadmium opposite the selenium coated disc, and the sputtering carried on as above described. The cell may then be sputtered with the gold and platinum.

As a modification of the above described process I have found that the sputtering can be carried on with an electrode such as that illustrated in Figure 4. A cadmium disc I0 isprovided with platinum inserts 4I and gold inserts 42. In the use of such an electrode. the sputtering current and other variables are controlled to bring the temperature of the disc above 200 C., thus `accomplishing the annealing and the sputtering simultaneously.

The cell shown in Figure 6 results from thismethod of formi-ng the layers on the selenium.

. A base 60 carries'a layer of selenium, 6I, 'over- .final layer can be considered as a combination barrier and electrode, as it performs both functions. The-usual connections can be made to this layer in the usual fway. s

I claim:

1. A'photoelectric cell of the selenium type includinga selenium coated back electrode, and' a translucent counter electrode overlying the back electrode and including a homogeneous mixture of platinum and gold in the ratio of substantially five to one.

2. A photoelectric cell of the selenium type comprising a selenium coated back electrode, a blocking layer thereon comprising a' semi-transparent layer of selenium and selenium oxides, a semi-transparent layer of cadmium and cadmium oxides overlying said blocking layer, and a semi-transparent layer of a homogeneous mixture of platinum and gold overlying the layer l of cadmium and cadmium oxides, forming a counter electrode. u

13. .A photoelectric cell of the selenium type comprising a selenium coated back electrode, a blocking layer thereon comprising a semi-transparent layer of selenium and selenium oxides, a semitransparent layerof cadmium and cadmium oxides overlying said blocking layer, 'and a semitransparent layer of a homogeneous mixture of 4platinum and gold in the ratio of about five to one overlying the layer of cadmium and cadmium oxides, forming a counter electrode.

ERIC Lrnow. v 

